Re: Newbie question...

Amund Trovåg wrote:

> Mike Atkinson wrote:
>
> > Amund Trovåg wrote:
> >
> > > Yes, thank you so much for that! This works, and I understand why it 
> > > should be like this.  :)
> > > The last problem I have now is the part of the expression that is 
> > > "relationName". In the language, the relationNames/relation 
> > > expressions, are always enclosed in parentheses like you show above. 
> > > The parentheses however, are not part of the actual string of the 
> > > token, they are rather there to show that it is a relation, and not 
> > > attribute e.g.
> > >
> > > This problem seems similar to the one you just solved, but it doesn't 
> > > seem to be(at least not in my newb experience) :).
> > > I have defined the tokens
> > > | <LEFTPAR: "(">
> > > | <RIGHTPAR: ")">
> > > and <RELATION> is the same as the token <ID>, only a different 
> > > tokenname.
> > >
> > > So I have:
> > > void project() #PROJECT:
> > > {Token t = new Token();}
> > > {// project + attribute name commalist(zero or more(*)) end with 
> > > //(relationname) and EOF=;
> > > (t=<PROJECT>) [attributeList()] Relation() {jjtThis.setToken(t.kind, 
> > > t.image);}
> > > }
> > > and the relation production:
> > > void Relation() #RELATION:
> > > {Token t = new Token();}
> > > {
> > >     t=<RELATION>{jjtThis.setToken(t.kind, t.image);}
> > > }
> > > In Relation() I want to do something like this:
> > > <LEFTPAR>t=<RELATION>{jjtThis.setToken(t.kind, t.image);}<RIGHTPAR>
> > > but this doesn't seem to work.
> > >
> > > When I write in the parser: project ssn, name(relationName); The 
> > > parser returns, "expecting <RELATION>". I get it to work if I define 
> > > the <RELATION> token to be enclosed by <LEFTPAR> and <RIGHTPAR>. 
> > > Still, this is not what I want. This token too, should have the 
> > > string as the relationName in itself, _without_ the parentheses.
> > >
> > > This may seem easy for some of you, but I would be happy if you could 
> > > point me in the right direction for this as well so I can get on with 
> > > my program.
> > >
> > > Thanks in advance,
> > >
> > > regards,
> > > Amund
> >
> > After parsing name it then tries to match Relation(), the first token of
> > Relation is <RELATION> while the next token of the input is "(".
>
> I didn't understand exactly what you mean here... Isn't the first token 
> of Relation() actually <LEFTPAR>, then <RELATION>, and then <RIGHTPAR>?
>
> > The answer is similar to the previous one. You need to change Relation()
> > to look for "(" <RELATION> ")".
>
> Yes, this is what I have been trying to do, with things like:
>
> void Relation() #RELATION:
> {Token t = new Token();}
> {
>     <LEFTPAR>t=<RELATION>{jjtThis.setToken(t.kind, t.image);}<RIGHTPAR>
> }
> It seems so easy to do, and I feel this _should_ be correct, but it 
> isn't :S
Think I may have found it! :)
The above expression is correct, however, only if I change the token 
<RELATION> with <ID> which has the same structure. Is it true that 
<RELATION> in the expression above calls itself recursively? (Because of 
#RELATION?) If so, I am a bit wiser today :)

Amund